In the last twenty years, cell phones have become ubiquitous with users purchasing cell phones for convenience as well as safety. Cell phone batteries have been developed with the objective of extending the battery life of the cell phone in both use (talk-time battery life) and when unused (standby). Cell phone talk time battery life ranges from less than two hours to more than ten hours, depending on the phone. The objective of extending the battery life responds to consumers who demand longer and longer talk time battery life and reduced need to charge the phone. At the same time, cell phone users are seeking smaller and more compact cell phones, which increase the challenge for battery manufacturers as they are being asked to increase talk time battery life in a smaller and smaller battery. By merely looking at the size of cell phones and reviewing their reported talk time batter life, it is evident that cell phone battery manufacturers have responded well to the demand for smaller batteries with longer talk time battery life.
Cell phones offer more than just convenience, of course. Many users carry a cell phone as a safety measure. For example, cell phone users rely on their cell phones to make telephone contact for assistance in the event of car problems, to seek assistance in dangerous situations, to seek aid in response to emergency medical needs, etc.
Cell phones typically have an alert system to ensure that users know when their phone's battery life is low. A common means of alerting the user to a low battery condition is by a warning beep and/or a display on the screen alerting the user to a low battery condition. The user knows at that time that very little talk time remains and the phone should be connected to a charger to recharge the battery. If the phone is not connected to a charger, the battery will eventually discharge even if left in standby mode. This is a problem when a user is not carrying the phone and it is left unattended in standby mode, e.g., the owner leaves the phone in a car in a briefcase, jacket or purse. In these situations, when the warning beep is sounded the user does not hear it and the phone battery completely discharges without the user knowing. Upon later needing the phone, such as in an emergency situation, the user likely will not have any battery power remaining to turn on the phone.
As illustrated in U.S. Pat. No. 7,388,349 it is known to add a reserve battery to a car battery to provide an emergency starting ability if the primary battery is dead or fails. The '349 Patent discloses a rechargeable battery system that includes a main battery and at least on auxiliary battery. According to the patent, the battery system is for a vehicle battery system in which the batteries are configured to fit within a housing having conventional external dimensions. The system also may include an attachment for attaching an auxiliary battery to a conventional battery and further include circuitry for switching between the main battery and the auxiliary battery. It should be noted that a car battery differs from a cell phone battery for a number of reasons. For example, a car battery is not drained during use but instead is constantly recharged during use by an alternator. As such a reserve car battery is useful when the primary car battery fails to start the car, such as a battery or alternator failure. In contrast, a cell phone battery is designed to be drained during use and later recharged.
Other dual battery systems also are known. For example, U.S. Pat. No. 5,223,351 discloses a dual battery system that includes a first battery and a second battery electrically connected in parallel to positive and negative terminals with the first battery having an open circuit voltage greater than that of the second battery so that, as current is drawn from both batteries, the amount of current drawn from each respective battery at a given voltage level varies depending on the magnitude of the current. The first battery preferably supplies most of the current at low to moderate current loads, whereas the second battery provides a greater portion of the total current at high current loads.
U.S. Pat. No. 5,487,099 discloses a portable telephone and an additional device for the portable telephone capable of improving the portability of the portable telephone. The additional device can be a battery that is attached to the existing battery of the telephone.
U.S. Pat. No. 5,973,477 discloses a multiple battery system used in a cell phone. The system includes a charging battery unit with multiple batteries that is connected to a buzzer and a high-voltage generator, both of which capable of forming a loop with the charging battery unit when the press switch is pressed. The high-voltage generator is connected to an electric guide rod controllable by a push switch to extend from or retract into the battery casing.
U.S. Pat. No. 6,037,756 discloses a power supply having a high energy capacity battery module and a high energy power battery module for providing power to a load. The high energy capacity battery module is connected to a DC to DC converter via a first switch for selectively providing power to the load. The high energy power battery module is connected to the DC to DC converter via a second switch for selectively providing power to the load.
U.S. Pat. No. 6,049,141 discloses a multi-battery system that includes a device and a method to allow multiple batteries with varying capacities and power capabilities to drive a common load. The method also adjusts the output current of one or more of the batteries driving a common load to maximize the operational time of the load. The level of the current being supplied by the battery unit is monitored and compared to a desired current level. Upon detecting a change in the level of the current, the output voltage of one or more of the battery systems is modified to return the level of the battery current to the desired current level.
U.S. Pat. No. 6,709,784 discloses an external backup battery for use with a cell phone or other device having a rechargeable battery and system that allows the battery to be recharged while still in the device. The backup battery plugs into the recharger connector on the cell phone and permits the backup battery to charge the main battery, thereby extending the life of the main battery.
U.S. Pat. No. 6,668,179 discloses a system and method for providing emergency reserve battery power. The system includes a detector that detects battery power level and causes the system to go into an emergency power reserve state that queries the user to determine if the call is an emergency call before making the call. The patent states that the battery reserve features may reserve a special portion of the battery, e.g., 5% or 10%, for only emergency situations.
U.S. Pat. No. 6,236,181 discloses a supplemental power vehicle for a radio controlled car. The supplemental power cell increases the top end speed of the vehicle and is generally a battery or batteries that are provided between the power supply for the vehicle and the motor that powers the vehicle.